


you came to me, could all be a bad thing

by WattStalf



Series: Commissions [304]
Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Aged-Down Byleth, Dubious Consent, F/M, Vaginal Fingering, Vaginal Sex, commission
Language: English
Status: Completed
Published: 2020-12-20
Updated: 2020-12-20
Packaged: 2021-03-10 21:26:30
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 3,071
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28193928
Author URL: https://archiveofourown.org/users/WattStalf/pseuds/WattStalf
Summary: A mishap leaves Byleth younger than any of her students, and Dimitri only plans to watch over her, same as the rest of his classmates.
Relationships: Dimitri Alexandre Blaiddyd/My Unit | Byleth
Series: Commissions [304]
Series URL: https://archiveofourown.org/series/1325462
Kudos: 33





	you came to me, could all be a bad thing

The professor just barely seems to know who she is right now. Dimitri is not able to figure out what, exactly, has happened to her, or how much it has effected her. The only thing that he knows for sure is that this is the direct result of Claude deciding it would be hilarious to trick Lysithea into using some incredibly advanced spell, telling her that it would be something entirely different.

She never meant to make Byleth suddenly younger, but now, they just have to wait for it to wear off, since that is the only solution given in book that it came from. Lysithea has tried a bit to reverse it, but eventually even she had to give up, but she promises Dimitri that she will not let her house leader off the hook for tricking her into de-aging the Blue Lion’s professor.

So now Dimitri and his classmates are left with an approximately thirteen-year-old professor. She really isn’t _that_ young, considering Lysithea herself is only fifteen, and Cyril, who has recently joined their class, is just fourteen. The age itself isn’t a problem, but it seems like she has lost some memory along the way, in ways that are hard for her to describe, or for Dimitri to understand.

She knows who she is and who they are, but does not know nearly as much about battle, or any of the things that she is supposed to teach them, and does not seem aware of the fact that she is their teacher, despite recognizing her class. It is hard to tell where her mind is right now, so they decide that it is not safe to let her wander around on her own, and that someone always needs to look after her, until the spell has worn off. Unfortunately, her father is away on a mission for the church right now, so that rules that out, and they are not sure if this is something that they want the church finding out.

Of course, it _is_ tempting to rat Claude out for what he has done, but ultimately, the class agrees to just keep Byleth away from any church officials for a while. Though they could probably have trusted Jeralt with her, he is not an option right now, so it is up to them to make sure she stays out of harms way, and out of Seteth’s line of sight.

“She can share my room,” Mercedes offers right away, not minding at all. “If this lasts overnight, she can spend the night with me, every night until she returns to normal.”

“Well, that solves that. The rest of us can take shifts keeping an eye on her when we aren’t in class,” Dimitri says. There are some who are not so enthused about babysitting duty, but even Felix can’t deny that he would feel bad if anything happened to Byleth because any of them happened to slack off, so he is able to get everyone on board.

For the most part, they just stay in the classroom when they are supposed to be in class, keeping the doors locked so that they have no surprise visits from anyone outside of their class. Flayn is eager to agree to keep the secret from her older brother, and with enough convincing, Cyril finally promises not to tell the archbishop, but only if they keep studying during their class time, and only if this does not last more than a few days.

Everything is going off without a hitch, and Dimitri is glad for that. However, once class is out and he is tasked with bringing Byleth food in the classroom and sitting with her for a bit, he starts to wonder about all of this. He does not like where his thoughts wander to, but he is not able to stop himself, not when he has had his mind on the new professor for so long.

Things should be different now that she is suddenly four years younger than him, rather than four years older. She looks so different, while also essentially looking the same; she still has that same, almost empty look in her eyes, and still has the same hair, and is still absolutely beautiful, but she is small now, around Cyril’s height, with skinny shoulders, and a body that has not yet started to develop.

Even thinking of something like that is enough to make Dimitri blush furiously as he carries a plate back to the classroom, careful to make sure no one important notices him to question what he is doing. He would be a little too dense to not notice how gorgeous Byleth is, in the form that he is used to, and he has spent plenty of time _noticing_ her body as it used to be.

Maybe it is not that strange to make comparisons between she is now and how she is supposed to be, but what is strange is the idea that he might not be that put off by the sudden change. If he allows himself to dwell on it for too long, he can’t pretend that his crush on Byleth has just vanished because she has gotten younger, nor can he pretend that he only feels this way because of how much he likes her as an adult. He can’t pretend that his feelings are not just as intense when he sees her as a child.

And he really, _really_ does not like where his thoughts go once he reaches that conclusion. For the brief time that he has known her, he has wanted her more than he has ever wanted anything in his life, and Dimitri has done everything in his power to keep that to himself, to keep even his closest friends from figuring it out. It has started to consume his every thought, in ways that only his darkest of impulses ever do, the parts of himself that he does not like.

Byleth looks at him in ways she did not before, something to do with just how dependent that she has become. There is just something _different_ about her now, something that makes it difficult not to wonder just how far he could take things. She seems so much easier to…

“Thank you for taking care of me,” she says, her voice still as level as he remembers, though there is so much youth to it now. “All of you have been so helpful.”

“We just wanted to return the favor,” he replies, glad that she can’t tell exactly what is running through his mind right now. “You do so much to take care of all of us.” A troubled expression comes over her face then, like she is trying to remember specific instances, but that does her no good. She really can’t seem to access key memories right now, but it still makes no sense to anyone just how this spell has effected her.

There is silence while she eats her dinner, and Dimitri tries to calm his thoughts, which continue to try and rage out of control. He is able to put on such a friendly face at school, able to keep so many of his darker thoughts to himself, but things have been so much worse since meeting Byleth. He has never wanted anything like he wants her, and it mingles with his dark impulses in the worst way possible, and now she is so small and vulnerable and trusting, and he should not be allowed around her, but of course he could never explain something like that to his classmates.

Besides Felix, he doubts any of them would even believe it, but if they did, it would ruin their opinion of their house leader, as well as their future king. Besides, he should be able to be trusted around her. He should be able to control himself, no matter what darkness may be lurking beneath the surface, because he does care about Byleth, really and truly. In his heart, he never wants to do anything to hurt her, not even if that means having her all to himself. The problem is just that his mind does not always agree with that, and his thoughts seem to move on their own, pushing him closer and closer to crossing lines that he knows should never be crossed.

“Thank you, again,” Byleth says, snapping him out of his thoughts. He realizes that she is done eating now, that it is time for him to take her dishes and return them to the dining hall, and probably time to hurry her along to the dorms, so that she can get settled in with Mercedes. She is probably not expecting Byleth quite so early, but there is not much else that she can do, not without being seeing.

Instead of doing any of those things, he closes the distance between them, pulling Byleth to her feet. As she looks up at him with a stunned expression on her face- who knew she was this _tiny_ at the age of thirteen?- he leans down to kiss her, even when he knows that this is the absolute last thing he should do to her. He is going to ruin everything, he is going to make her hate him forever…if she even remembers any of this.

It is a stupid and irrational thing to think of, but it has been nagging at him this whole time. Her memory is so fuzzy as it is, so what if she does not remember what happened, once the spell has worn off? There is an equal chance that she _will_ remember, and that has helped hold him back, but the thought that she might not kept pushing him forward, and now he is holding her so close to him, practically crushing her body in his arms- but not quite, he is doing his damnedest to be careful of that, even if he is unable to control anything else right now.

Then Byleth, still stiff in her arms, tries rather clumsily to kiss him back. Though Dimitri has little experience himself, it is clear that Byleth has absolutely no idea what she is doing, and is still trying to return it. Is that because she wants to, or out of some sense of obligation, because he kissed her first? He somehow doubts it would be the latter, and not just because of his wishful thinking. Byleth does not seem like the sort who would try and do something like that out of mere obligation.

Whatever the case may be, she has sealed her own fate by returning his kiss, because there is no way that he can hold back now. Not when they are already alone in the classroom, where he has plenty of time before anyone starts to wonder where she is, not when no one outside of his class even knows where to look for her, not when they are all being careful to not call attention to the situation at hand.

The circumstances seem to be absolutely perfect for him to take advantage of what is going on, to take advantage of his suddenly young and naive professor. Young, naive, and helpless, and for whatever reason, kissing him back, even as he starts to grow more aggressive with it, clinging to her and moaning into her mouth, needy and possessive. He has never wanted anything more than he wants her, has never _needed_ anything this much, and there has always been this part of him that thinks, so irrationally, that everything would be better if only he had her.

He knows that will change nothing, and he knows that he can’t actually possess her, that he can’t truly possess anyone. And even so, he continues hoping for that to be the case, and now he has this perfect opportunity to make her his, right in front of him. Dimitri is not going to be able to stop now.

When he breaks the kiss, her voice is soft as she breathes, “Dimitri…” There must be at least some part of her that understands how wrong all of this is, that he should not be making these overtures at any time, but least of all when she is so young. But she does not do anything to protest when he starts working to get her out of her clothes, wondering just how thorough the spell is to have shrunk them down with her, still a perfect fit.

“I’m just taking care of you,” he replies, surprised by how level his voice sounds right now, as if this is natural for him. “Just like you take care of all of us.” It’s a terrible excuse for this, and she must know that, but she decides to go right along with it, and does not stop him from undressing her, not even as the last of her clothing falls to the floor, leaving her completely naked and vulnerable in front of him.

He struggles to hold himself back when looking at her like this, wanting to just pin her to the floor and take her then and there. Instead, he goes to sit at one of the desks, not even his own though he tries not to remember who it normally belongs to, where he gestures for her to sit on his lap. As he holds her there, he is able to push her legs open, and a reach a hand between them, a little surprised by how wet she is. He had noticed her getting into the kiss, but even so, he had no idea that she would be _this_ into it, and that is almost enough to make him think he is not doing such a bad thing with all of this.

Almost, but he still knows the truth, and can’t convince himself that easily. Even so, nothing is going to stop him, especially not once he has started touching her, making her whimper for him. It is such an adorable sound, and so unlike the stoic professor that he has fallen so hard for, and that only makes it that much more endearing. There is, perhaps, a part of him that would not mind if she stayed like this forever, not only because she is a bit easier to have his way with, but because he does like her like this, a fact that he is not sure he wants to try and unpack.

His fingers are a bit clumsy at first, but steadily, he is able to figure out what it is that she likes, and he gets a bit better at it then, managing to make her moan more and more for him, sounds that he knows he could never get tired of. For the time being, he is not going to think about the future or what comes after the spell wears off, because for right now, Byleth is all his, and that is all that matters to him.

His patience can’t hold up forever, but he does his best to at least hold up until she is panting for him and even wetter than when he first touched her, practically going to pieces in his arms. Then, he nudges her out of his lap, where she struggles to even stand on her own, for the short time that it takes to undo his pants so that he can pull her back onto his lap, facing him this time.

He should probably let her face away, like he did when he was fingering her, worried that this might remind him of his guilt. That is what he thinks, but as he pulls her down onto his cock, slowly, taking his time to penetrate her, he realizes that he has nothing to worry about there. Even looking into the youthful face of his professor is not enough to overwhelm him with guilt right now, his guilt having taken a back seat to his pleasure for the time being.

Byleth is so tight, and it is so hard to be patient as he lets her get used to it all, never giving her more than she can handle, but then he is completely inside of her, as deep as he can do, and she is whining on top of him. If she is in any pain, she has decided that she much prefers the pleasure, which is something that he is inclined to agree with. Holding her steady by her hips, he begins to thrust up into her, slowly at first, still giving her time to adjust to these things.

The pleasure is immense and overwhelming, but not quite as overwhelming as what happens once Byleth is able to regain her composure. Which is planting her hands on his shoulders and leaning in to press her lips to his while she pushes herself up and down, promptly breaking the kiss she has initiated as she starts to ride him. From then on, Dimitri does not have to worry about giving her more than she can handle, because she takes care of that on her own, letting him sit back while she stuns him with how eager she is to take control.

That does not mean anything about her actual consent in the matter, and does not make him any less scummy for taking advantage of her, but in the moment, it really does make him think this is not so bad, and that there might be something to this, something to indicate that Byleth, somewhere below the surface, deep enough to carry over when so many things did not, has actually been wanting this as well.

Whatever the case, he lets her use him to her heart’s content, until she is moaning, low and desperate, as she shudders with her orgasm, and he clings tight to her as he joins her in that, unable to hold back for even a second longer. For a long time, they sit in silence, with Dimitri holding her small form close, before either can think about what to do next.

As for Dimitri, he has no idea where to go from here, or if this will even matter that much, in the grand scheme of things, if she really ends up not remembering it. But he can’t undo what he has done, so he will just have to face whatever comes his way.

**Author's Note:**

> If you're interested in my writing updates, please follow my fanfiction twitter @WattStalf


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